Hereditary spastic paraplegias (SPG) are a group of neurodegenerative diseases clinically characterized by progressive lower limb spasticity, hyperreflexia, and paresis. SPG may be inherited in an autosomal dominant, autosomal recessive, or X-linked recessive manner, with the majority presenting as autosomal dominant SPG (Fink, J. K. and Hedera, P., Semin. Neurol. 19(3):301-9 (1999); Tallaksen, C. M. et al., Curr. Opin. Neurol. 14(4):457-63 (2001)). Eleven different chromosomal loci have been identified for autosomal dominant SPG (Reid, E., J. Med. Genet. 40, 81-86 (2003); Orlacchio, A. et al., Ann. Neurol. 58, 423-429 (2005). Five genes underlying autosomal dominant SPG have been discovered: spastin (Hazan, J. et al., Nat. Genet. 23:296-303 (1999)); atlastin (Zhao, X. et al., Nat. Genet. 29:326-331 (2001)); HSP60 (Hansen, J. J. et al., Am. J. Hum. Genet. 70:1328-1332 (2002)); KIF5A (Reid, E. et al., Am. J. Hum. Genet. 71:1189-1194 (2002)); and BSCL2 (Hiltunen, M. et al., Neurosci. Let. 250:69-71 (1998)). Further genetic heterogeneity has been suggested (Ashley-Koch, A. et al., Neurogenetics. 3:91-97 (2001)). A need remains for means to distinguish the variants of SPG from one another.